Doing warm up exercises before you workout is important in many ways. A good warm up will gradually increase your heart rate, increase circulation to your muscles, tendons and ligaments, and mentally prepare you for your workout. You want to physically prepare your body for the demands of a strenuous workout by gradually increasing your body temperature. Warm up exercises are also important as a form of mental preparation. Your mind can ease into the workout. This is especially helpful if you engage in strenuous forms of exercise such as lifting heavy weights or taking an advanced group fitness class. Your muscles warm up to prevent injury. Your ligaments and tendons become more flexible, reducing the chance of injury.